A phototube, or photoelectric cell, or photo-emissive cell, may be a sensitive detector of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum.
A photomultiplier tube is a vacuum phototube that is able to multiply the current produced by incident light by many times, thus enabling individual photons to be detected when the incident flux of light is very low. Photomultiplier tubes have important applications in nuclear and particle physics, astronomy, medical diagnostics including blood tests, medical imaging, motion picture film scanning, radar jamming, and high-end image scanners known as drum scanners.
A conventional photomultiplier tube (PMT) includes a housing containing a photocathode, several dynodes and an electron collector. Light entering the tube and incident on the photocathode causes electrons to be emitted by the photocathode, as a consequence of the photoelectric effect. The electrons impinge on the successive dynodes, causing electron multiplication by secondary emission. After impingement on the last dynode, the electrons are collected by the collector and used for detection of the incident light.
Although the successive dynodes help to increase the number of electrons reaching the collector by secondary emission, the successive dynodes also make the conventional PMT huge, heavy, and difficult to produce.